PWM Inverter Synchronization for Conducted Emission Reduction
Solution Overview
Problem
High frequency switching in motor drive inverters generates undesirable AC electrical content and harmonics, leading to conducted emissions that interfere with other electrical devices and require costly line filters to mitigate, especially in systems with multiple motors and drives.
Innovation Solution
The inverter's PWM routine is synchronized with an external signal, allowing the switching periods to be aligned either at the start or midpoint, reducing overall conducted emissions by coordinating the switching intervals across multiple inverters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high frequency switching is used in PWM inverters to control motor voltage magnitude, then the output voltage control precision is improved, but conducted emissions increase causing interference with other electrical devices
Solution Approach 1:
Multiple inverters are synchronized to operate with coordinated switching periods, merging their operations to produce constructive interference that reduces overall conducted emissions. The inverters share a common switching frequency and are timed to switch at complementary moments, transforming individual harmful emissions into a reduced collective emission profile.
Solution Approach 2:
The invention employs periodic synchronization of switching periods across multiple inverters, where each inverter operates at a high frequency but coordinates its switching events to occur at specific periodic intervals. This periodic coordination allows the high frequency switching to maintain precise voltage control while the synchronized timing reduces the cumulative conducted emissions.
2Object-affected harmful factors
If line filters are added to prevent conducted emissions from being transmitted back to AC input voltage, then electromagnetic compatibility is improved, but system cost and space requirements increase
Solution Approach 1:
The invention converts the potentially harmful high frequency switching emissions into a beneficial reduced emission profile by synchronizing multiple inverters. Instead of treating emissions as a problem to be filtered out, the system uses coordinated switching to make the emissions naturally reduce, thereby improving electromagnetic compatibility without requiring additional filtering hardware.
Solution Approach 2:
The synchronization mechanism preemptively coordinates switching events to prevent the buildup of cumulative conducted emissions before they can cause interference. By anticipating and preventing the emission problem through coordinated timing, the system avoids the need for corrective filtering measures.
3Productivity
If multiple inverters are used to control multiple motors, then system productivity is improved, but total conducted emissions increase requiring larger filters
Solution Approach 1:
Multiple inverters operating to control different motors are merged into a synchronized system where their switching operations are coordinated. This merging allows the system to maintain high productivity with multiple motors while the coordinated switching reduces the total conducted emissions, eliminating the need for larger filters that would otherwise be required.
Solution Approach 2:
The synchronization mechanism provides a universal solution that enables multiple inverters to operate together without increasing total emissions. Each inverter maintains its independent motor control function while participating in the coordinated switching scheme, achieving multi-functionality without the penalty of increased electromagnetic interference.
Data Source
AI summary
An inverter executing a PWM routine is configured to synchronize the switching periods of the PWM routine to an external signal. The external signal is generated, for example, by another inverter, a converter, or a high level controller. The external signal is preferably generated periodically, and the switching period is resynchronized to the external signal each time the external signal is received. Optionally, either the start time or the midpoint of the switching period may be aligned with external signal. Further, the external signal may be sent to multiple inverters. Preferably, a first portion of the inverters align the start time of their respective switching period to the external signal and a second portion of the inverters align the midpoint of their respective switching period to the external signal.